Safety paper and the manufacture thereof



' Patented Nov. 18, 1941 SAFETY PAPER AND THE MANUFACTURE THEREOFFrancis L. Simons, Montclair, N. J., assignor to George La Monte & Son,Nutley, N; 3., a corporation of New Jersey No Drawing. ApplicationSeptember 2a, 1938, Serial No. 232,082

21 Claims.

This invention relates to safety paper including fraud-preventingwriting material made of paper or other substance or composition adaptedfor printing or lithographing or for the inscription of writing thereonand for use, for example,

.in the manufacture of checks, drafts, bonds,

stock certificates or other instruments which it is desired to haveprotected against fraudulent alteration. This invention also relates tomethods of making such paper.

There are many chemical substances which are known and which have theproperty, when incorporated with paper during the manufacture thereof orby impregnation therein or superficial application thereto, ofdeveloping a disfiguring stain upon the application of a chemical inkeradicator thereto by changing from a colorless to a colored substance,by becoming more intensely colored or by change in color or the likewhen the chemical ink eradicator is applied to the paper. The developedstain that results upon application of a chemical ink eradicator to thepaper makes obvious any attempt by means of a chemical ink eradicator toalter or tamper with the paper. Some chemicals such as manganesesulphate, iodides, etc., change color when a bleaching agent is appliedthereto but can readily be converted back to their original condition byapplication of a reducing agent. Other chemicals, however, such as thechemicals specifically .mentioned hereinbelow after having their colorchanged by the application of a chemical ink eradicator thereto cannotbe readily reduced to their e original color and afford a record ofattempted alteration of the paper that and 1,535,863 the use of primaryamines such as benzidine, tolidin, dianisidine, and diphe'nylamine. andtheir derivatives is described. In Patent No. 1,839,995 aryl substancesreferred to therein as guanidine substances," e. g., diphenylguanidine,are described as stain-producing substances for use in safety paper. InPatent No. 2,061,632, there is disclosed a large number ofamino-aryl-thiazoles, reference being made particularly tol-amino-aryl-thiazoles in which the v amino-nitrogen is directly bondedto the carbon 55 coloration.

of the thiazole ring and has at least one free amino-hydrogen and inwhich the aryl'group contains at most two benzene rings.

It is a purpose of this invention to incorporate stain-producingsubstances such as the stain-producing amines in safety paper in such away that thorough impregnation is facilitated while at the same timeeifecting a very permanent incorporation of the substance in the Paper.It is a further purpose of this invention to incorporate in safety paperacidic derivatives of stainproducing amine substances without adverselyaffecting the quality and ageing characteristics of the paper. It is afurther purpose of this invention to incorporate stain-producing aminesubstances in safety paper in conjunction with ferrocyanide as anink-fixingsubstance in such a way that the ferrocyanide does notdecompose prematurely and discolor the paper.

Ferrocyanides, when incorporated in safety paper have the property offorming with iron compounds in ink certain deeply-colored compoundsknown as Prussian blue, the exact chemical nature of which is notcertain and may vary to some extent, depending upon the proportions andcharacter of the reacting substances. Prussian blue is highly resistantto ink eradicators in general use at the present time. The most commonlyused ink eradicators have a chlorine bleach as a .basis. Another type oferadictor has potassium permanganate as a basis. The latter eradicatoris normally followed in actual use by the application of some reducingagent such as sodium bisulphite to clean up the manganese dioxidedeposited during the application of the permanganate. The Prussian blueformed by by writing with ordinary iron-containing ink on safety paperprepared with a ferrocyanide is resistant to the action of either of theeradicators referred to. The Prussian blue is especially resistant tothe potassium permanganate type of eradicator. While the Prussian blueis also resistant to a chlorine bleach type of eradicator when the colorhas been developed to a relatively pronounced degree, faint colorationsuch as that produced when a very small amount of ferrocyanide isincorporated with safety paper can be affected to some extent by thechlorine bleachtype of ink eradicator.

The stain-producing amine substances mentioned above react merely with,the chlorine bleach type of eradicator to produce disfiguring stains.They do not react with the potassium permanganate type of eradicator toproduce dis- The stain-producing amine substances which have beenmentioned above are commonly used in a Water-insoluble condition. Thestain-pro ducing amine substances when so used are generallyincorporated with the pulp in the beater during the manufacture of thesafety paper. This method of incorporating the chemical in the safetypaper is not altogether satisfactory inasmuch as there is considerableloss of the safety chemical during the formation of the paper from thepulp. Moreover, it is frequently desirable to treat paper that hasalready been manufactured so as to make it sensitive to chemical inkeradicators and this is difi'icult when'a waterinsoluble chemical is tobe used.

There are water-soluble forms of stain-producing amine substances, thewater soluble acid salts of such substances being the most common,

presence of li ht and tend to decompose so as to prematurely discolorthe safety paper; Moreover, the water-solubility of such substancesmakes it possible to wash such substances out of the safety .pamr, thusdestroying the effectiveness of the safety paper. The fact thatstainproducing amine substances can be successfully washed out of safetypaper is a serious drawback to the 'eiiectiveness or the protectionafiorded by these materials.

According to one of the features of this invention a stain-producingsubstance such as a stain-producing amine is incorporated in safetypaper while in a water-soluble acidic form and is converted into awater-insoluble form while incorporated in the safety paper byneutralizing the acidity of the substance. For example, a stainproducing amine substance is incorporated in the safety paper in theform of a watersoluble acid salt and, while -it is incorporated in thesafety paper, is treated to transform it into a water-insolublestain-producing amine substance by neutralizing the acidity of the acidsalt added to the safety paper. Other stainproducing substances such asstain-producing.

thioureas and their amino-derivatives may be incorporated in a similarway. .It is another feature of this invention that caustic alkali,neutralization in this manner is regarded as much less desirable thanneutralizathe neutralization of a water-soluble acid salt of astain-producing amine substance is accomplished while it is incorporatedin the, safety paper by means of a buffer mixture. The. buffer isefiective to overcome the acidity of the stainproducing substance andhas the greatadvantage of not being injurious in any way to the paper;

This invention may be illustrated, for example, in connection with thesubstance l-amino-5- chloro-benzo-thiazole. This substance whileinsoluble in water, is water-soluble when in the form of thehydrochloride. According to this invention1-amino-5-chloro-benzo-thiazole hydrochloride in aqueous solution isadded to safety paper and then is-transformedto insoluble form.

"For example, the hydrochloride is added to safety paper which containsa bufler such as a mixture aaeaeaa of mono-sodium phosphate anddi-sodium phosphate or a mixture of borax or boric acid, or is added tothe paper first, the paper thereafter being treated with the buffer. Ineither event the. 1- amino- 5 -chl0ro-benzo-thiazole-hydrochloride whileincorporated in the safety paper is transformed by the louder from thewater-soluble acid salt to a water-insoluble form. This is of advantagefor the reason mentioned above, namely, that while the water-solublehydrochloride is readily incorporated in the safety paper, it isrendered insoluble so, that it is very dificult to remove thestain-producing substance from the paper by washing the paper withwater. It is of even greater practical importance that the aging qualityof the paper is improved. When the l-amino-E-chloro-benzotmole-hydrochloride is applied to the paper,

it includes the hydrochloric acid forming partof the molecule and inaddition 50?.19 free-hydrochloric acid which is necessary for thepurpose of keeping this substance in solution. The solution as appliedto the paper usually has a pH value below 4 and usually has a pH valueof about 3. This causes the paper which is normally somewhat acid anywayto be removed from the bath in a distinctly acid condition. Thisadditional acidity of the paper has a tendering effect upon the paper.The age resistance of the paper can be improved by increasing the pHvalue to about 5.5 and even a lesser degree of acidity than this is tobe preferred for papers designed for long life.

The neutralization by means of a bufier of the acidity imparted tosafety paper as a r'esultof the addition to the paper of an acid salt ofa stain-producing amine substance is distinctly preferable according tothis invention. By causing the acid salt to react with the buffer, it isnot necessary to make the paper distinctly alkaline at any time or totreat the paper with strongly alkaline substances, nor is it necessaryto run the danger of underor over-neutralizing the paper. While it iswithin the scope of this invention to neutralize the acidity of an acidsalt of a stain-producing amine substance while the substance isincorporated in the paper by means of an alkali such as soda ash or adilute tion accomplished by a bufier mixture. When a straight alkali isused, it is injurious to many types of paper and is essentiallyinjurious to Paper which has been sized with the usual rosin sizing.Moreover, care has to be exercised in controlling the amount of alkalithat is-used.

I have iound that a ferrocyanide may be successfully incorporated insafety paper together with a stain-producing amine substance.Ferrocyanides tend to be unstable standing by themselves or in thepresence of an acid when applied to safety paper, with the result thatthe ferrocyanide decomposes so as to cause prematurediscoloration of lthe paper. In my Patent No. 2,037,937, the stabilization offerrocyanides incorporated in safety paper is described. The acidity ofan acid salt of a stain-producing amine substance tends to causepremature decomposition of ierrocyanide applied to safety paper. I havefound, however, that by incorporating a bufi'er with safety paper it ispossible .to makea stable safety paper which has been treated both witha water-soluble acid salt of .a stainproducing amine and with aferrocyanide.

T e use of a buffer containing alkali metal minor proportion ofmonosodium phosphate, it

is apparent that the disodium phosphate may be used by itself as abufl'er to counteract the acidic eflect of an acid salt ofa-stain-producing amine. Tri sodium phosphate may also be used but isnormally less desirable than the disodium phosphate due to its greaterdegree of alkalinity.

A safety paper that contains a stain-producing amine substance and aferrocyanide is extremely effective against all types of chemical inkeradicators'that may be applied thereto. While the stain-producing aminedoes not react with the permanganate type of ink eradicator, theinkflxing efiect resulting from the reaction of the ferrocyanide withink containing iron such as the ordinary blue-black iron 'gallotanatewriting ink is extremely resistant to the permanganate type of inkeradicator and afiords very effective protection, even when theferrocyanide is present in only a relatively small amount. If thechlorine bleach type of ink eradicator is applied to the safety paper,the stain-producing amine substance immediately produces a discolorationor stain of a permanent character that shows that the paper has beentampered with and in addition the ink-fixing action of the ferrocyanideaffords added protection when this type of ink eradicator is used.Therefore, a high degree of protection is afforded against both thepermanregarded as being particularly efiective and are relativelyinexpensive.

A further understanding of the preparation of safety paper according tothis invention will be apparent from the following specific examplewhich is illustrative of the practice of this invention. The paper isfirst treated with an aqueous solution of a water-soluble acid salt of astain-producing amine substance, e. g., 1-amino-5-chloro-benzo-thiazole-hydrochloride. A solution of about 4% to2% concentration of this substance is suitable for the purpose. Thepaper then may be dried or merely passed between squeeze rolls so as topress out its excess moisture and so as to make the surface of the paperfree of the solution. If the paper is not completely dried it ispreferable to'not only pass the paper between the squeeze rolls but alsoover a drying drum so that the surface of the paper may be free ofexcess solution of acidic character. The paper is then passed through abath containing about 5% of sodium ferrocyanide, about 12% of disodiumphosphate, and about 1% of monosodium phosphate. treating the paperwiththis second bath, the paper is passed between squeeze rolls so as toremove excess solution and then is dried. The paper is then ready foruse although further finishing, printing or ornamentation as desired maybe applied to the paper. The finished paper preferably has a pH of about6.0 to about 7.0 although satisfactory results are also obtained whenthe pH value is about 6.2 to about 7.3; but

these limits are not to be regarded as absolutely ganate type andagainst the chlorine bleach type of chemical ink eradicator. Moreover,due to the presence of the acid-alkali buffer in the paper, thestain-producing amine substance occurs in a water-insoluble conditionand cannot be washed out of the paper.

It is also of great practical importance that the paper cannot betreated so as to wash out the safety chemicals. It has been mentionedabove that stainyproducing amine substances can be washed out of safetypaper containing such substances in water-soluble form by washing thepaper with water. Even when these substances are in water-insoluble formthey can be washed out of safety paper by using dilute acid. Forexample, substances such as benzidine or 1-amino-5-chlor-benzo-thiazoleare soluble in dilute hydrochloric acid and substances such as guanidinesubstances are soluble in dilute acetic acid. When, however, aferrocyanide stabilized by a buifer is present in addition to thestain-v producing substance, it is impossible to wash out thestain-producing substance. If the paper is washed with a dilute acid,the acid immediately causes the ferrocyanide to turn dark blue and toreveal the" attempt to alter the'paper. Therefore, the new paper of thisinvention, due to the combination of safety chemicals used, not only iseffective against the different types of chemical ink eradicators whichmight be used, but also is effective against attempts to remove thesafety chemicals from the paper and affords much more effectiveprotection than that which has been regarded as possible heretofore.

In the practice of the invention using ferrocyanides, the solubleferrocyanides are preferable,

namely, the ferrocyanides of the alkali metals (including ammonium) andof alkaline earths. The ferrocyanides of sodium and potassium areessential to the practice of the invention. In the foregoing example,the proportions given are based on the weight of the fully hydratedcommercial salts that are added to the bath. The

bath containing ferrocyanide and monoand disodium phosphates has a pHvalue of about 7.0 to 7.4 when made up.

The sequence of operations mentioned above is regarded as preferablefrom the point of view of effectiveness and economy although the orderin which the chemicals are added to the paper may vary. For example, theferrocyanide and phosphate may be added to the paper prior to thetreatment of the paper with the acid salt of the stain-producing aminesubstance. In such case,

the acidity of the acid salt is neutralized as the salt becomesincorporated with the paper and while the salt is within the paper.

sheet in the manner above described, the solu-- tion can. of course, beapplied in any other manner as by spraying the sheet with thesolution,applying the solution locally by printing or otherwise, or in any othersuitable manner. Whether the substances are applied through the paper orat the surface, the same are to be regarded as incorporated with thesafety paper.

A stain-producing am ne substance can be incorporated at the time thepaper is tub sized by mixing th substance with the sizing bath. Thissubstance can also be included in a .dye bath and incorporated with thepaper during the application of the dye to the paper.

After Further in this connection. the treatment of the-paper with abuffer may be performed as a separate step at have in the safety paperan'amount of alkali metalphosphate or other bufier materialcorresponding to about 50% to about 300% of the combined ferrocyanideand amine substance in the paper. The amount of ferrocyanide that isincorporated in the paper may be increased to about 5%, the maximumamount that the paper retains when impregnated with a saturated solutionof a ferrocyanide. The proportion of stainproducing amine that is usedmay also be increased considerably, e. g., to about 1.0% by applying amore concentrated-solution thereof to the paper. In general the moreferrocyanide or stain-producing substance that is used, the morevigorous will be the ink-fixing property of the ferrocyanideand thestain-producing property of the amine substance. For purposes of economyit is preferable to use amounts such as those cyanide in the paper, theferrocyanide may be omitted. In such case the procedure mentioned in theforegoing example may be followed, using the disodium phosphate andmono-sodium phosphate mixture to convert the l-amino-S-chlorobenzo-thiazole-hydrochloride to an insoluble form. When the ferrocyanideis omitted, however, the advantages which result from the combinedpresence of stain-producing substance and ferrocyanide and which havebeen referred to above, are also omitted. While it is preferable tointroduce the stain-producing substance in water-soluble form andconvert it while incorporated with the paper to a water-insolubleformand combine the stain-producing compound in insoluble form with aferrocyanide, the stain-producing compound in insoluble form may be in-'corporated with the paper, as by mixing it with the pulp in the beaters,and thereafter adding the ferrocyanide to the paper to' achieve theadvantages that result from the combined presence of a stain-producingsubstance and. a ferrocyanide in the finished paper.

While this invention has been described in Y connection with specificexamples, it is to be un- 1. A method of making safety paper whichcomprises incorporating with paper 3 a watersoluble acid salt of anorganic aryl e adapted ,to react with a chlorine bleach to produce astain and converting said substanceto a waterinsoluble' form byneutralizing the acidity ,of said salt: a

being in the presence of said buffer when said organic amine iscontacted therewith.

3. A method of making safety paper which comprises incorporating inpaper a solution of a we.- ter-soluble acid salt of a stain-producingamino.- aryl-thiazole substance and neutralizing the acidity of saidsubstance to convert it into a water-insoluble form while said substanceis incorporated with said paper.

4. A method of making safety paper which comprises incorporating asolution of awater-soluble acid salt'of a stain-producingamino-aryl-tln'azole in paper containing a bufier.

5. A method of making safety paper which comprises incorporating inpaper a solution of a water-soluble acid salt of a stain-producingaminoaryl-thiazole and then treating the paper containing saidincorporated acid salt with a solution containing a bufier.

6. A method of making safety paper which comprises incorporating inpaper a solution of a water-soluble acid salt of a stain-producingamino-aryl-thiazole and then treating the paper containing saidincorporated acid salt with a solution containing a bufier and awater-soluble ferrocyanide.

7. A method of making safety paper which comprises incorporating inpaper a solution of a water-soluble acid salt derivative of benzidlneandneutralizing the acidity of said salt to convert it into awater-insoluble form while the substance is incorporated in said paper.

8. A method of making safety paper which comprises incorporating insafety paper a hydro-.

chloride of an organic aryl amine adapted to react with chlorine bleachto produce a stain, a ferrocyanide and a buffer, said hydrochloridebeing neutralized by action of said buffer while incorporated in saidpaper and said ferrocyanide being in the presence of said bufier whensaid hydrochloride is contacted therewith.

9. A method of making safety paper which comprises incorporating insafety paper l-amino- 5-chloro-benzo-thia'zole hydrochloride, an alkalimetal phosphate and aferrocyanide.

10. A safety paper having incorporated therewith a water-insolubleorganic aryl amine adapted to react with a chlorine bleach to produce astain, a ferrocyanide, and a buffer, the pH-value of the paper beingbetween about 6.2 and about 7.3. 11. A safety paper having incorporatedtherewith a water-insoluble organic and amine adapted to react with achlorine bleach to produce a stain, a ferrocyanid and a buffer.

12. A safety paper having incorporated therewith a water-insolubleorganic aryl amine adapted to react with a chlorine bleach to pro- 2. Amethodof making safety pape'r'which comprises treating paper with awater-soluble acid-salt of an organic arylamine adapted to react with achlorine bleach to'produce a stain, a ferrocyanide and a bufier, saidacid salt being neutralized by the action of said bufier whileincorporated in said paper and thereby converted into water-insolubleform anolsaid ferrocyanide --duce a stain, a ferrocyanide, and an alkalixfnetal with a stain-producing amino-aryI-thiazole, a

ferrocyanide, and an alkali metal phosphate.

15. A safety/paper having incorporated 1- amino-5-chloro-benzo-thiazolein insoluble form in the presence of a bufier and a solubleferrocyanide.

162A safety paper having incorporated lamino-5-chloro-benzo-thiazole ininsoluble form in the presence of an acid-alkali buffer and a solubleferrocyanide, the pH value of the paper .being about 6.2 and about 7.3.

17. A safety paper having incorporated therein a substance adapted toreact with a chlorine bleach to produce a stain, said substance beingselected from the group consisting of anilin, anilin chloride, benzidineand its derivatives that contain the benzidine nucleus, tolidin and itsderivatives that contain the tolidin nucleus, dianisidine and itsderivatives that contain the dianisidine nucleus, diphenylamine and itsderivatives that contain the diphenylamine nucleus, aryl guan'idinesubstances, and l-amino-arylthiazoles in which the amino-nitrogen isdirectly bonded to the carbon of the thiazole ring and has at least onefree amino-hydrogen and in which the aryl group contains at most twobenzene rings; and also having incorporated therein a ferrocyanide and abuffer.

18. A safety paper having incorporated therein benzidine, awater-soluble ferrocyanide, and a butler, the pH value of the paperbeing between about 6.2 and about 7.3.

19. A method of making safety paper which comprises incorporating withpaper' in watersoluble acidic form a substance adapted to react withachlorine bleach to produce a stain,

said substance being selected from the group consisting of anilin,anilin chloride, benzidine and its derivatives that contain thebenzidine nucleus, tolidin and its derivatives that contain the tolidinnucleus, dianisidine and its derivatives that contain the dianisidinenucleus, diphenylamine and its derivatives that contain thediphenylamine nucleus, aryl guanidine substances, andl-amino-aryl-thiazoles in which the amino-nitrogen is directly bonded tothe carbon of the thiazole ring and has at least one free amino-hydrogenand in which the aryl group contains at most two benzene rings; andconverting said substance to a water-insoluble form while the substanceis incorporated with the safety paper by neutralizing the acidity of thesubstance.

20. A safety paper having incorporated therein'diphenylamine, aWater-soluble ferrocyanide, 4

and a buffer, the pH value of the paper being between about 6.2 andabout 7.3.

21. A method of making safety paper which comprises incorporating inpapera solution of a water soluble acid salt derivative of diphenylamineand neutralizing the acidity of said salt to convert it into awater-insoluble form while the substance "is incorporated in said paper.

FRANCIS L. SIMONS.

CERTIFICATE OF comes-non. PatentNo. 2,262,822. November 1 19in.

FRANCIS L. sInoN's.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 1,first column, line 1414., for the patent number "1,556,861" read--l,555,861-"- and second column, line 56, strike out "by"; page 2,second column, line 2, for orax or" read --borax and-; page 14., secondcolumn, line 56, claim 8, insert "a" before "chlorine" page5, firstcolumn, line 5 claim 16, after "being" insert -betweenq and that thesaid Letters Patent should be read with this correction therein that thesame may conform to the record of the' case in the Patent Office.

Signed and sealed this 25rd day of December, A, D. 19l1l.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents.

